ASSESSMENT OF THE RESILIENCE POTENTIAL OF THE PALK BAY REEF THROUGH KEY INDICATORS
Thesis submitted to
Cochin University of Science & Technology
in partial fulfillment of the requirements for
the Award of the degree of
Doctor of Philosophy In
Marine Science
Under the Faculty of Marine Sciences
By
B Manikandan Reg. No. 4061
CSIR- National Institute of Oceanography Regional Center
Dr. Salim Ali Road, Post box No 1913 Kochi- 682018, INDIA
August 2015
Assessment of the Resilience potential of the Palk Bay reef through Key Indicators
Ph.D. thesis under the Faculty of Marine Sciences, Cochin University
Author
B. Manikandan DST-INSPIRE fellow
CSIR- National Institute of Oceanography Regional center
Dr. Salim Ali Road, Post box No 1913 Kochi- 682018, INDIA
Supervising Guide
Dr. J. Ravindran Senior Scientist
Biological Oceanography Division National Institute of Oceanography Donapaula, Goa - 403004
National Institute of Oceanography Regional center
Dr. Salim Ali Road, Post box No 1913 Kochi- 682018, INDIA
August 2015
Declaration
I hereby declare that the thesis entitled “Assessment of the Resilience Potential of the Palk Bay reef through Key Indicators” is an authentic record of the original research work done by me under the supervision of Dr. J. Ravindran, Senior Scientist, CSIR- National Institute of Oceanography, Regional Center, Kochi- 682018 in partial fulfillment of the requirements for the degree of Doctor of Philosophy in Marine Science and no part thereof has been presented before for the award of any degree, diploma or associateship or any other similar title in any other University or Institution.
Kochi - 682 016
August 2015 B. Manikandan
Dedicated to all those who
strive to conserve coral reefs
Statement of Contribution by Others
Some of the work I carried out for my PhD was collaborative and performed with technical, theoretical, statistical, editorial or physical assistance of others. I fully acknowledge the contribution of others as outlined below.
Chapter 2 & 5
These chapters contain research that made use of remote sensing based data on Photosynthetically Active Radiation (PAR) and Sea Surface Temperature (SST). Mr.
Mani Murali, Scientist, Physical Oceanography Division, CSIR- National Institute of Oceanography and Dr. P. J. Vidya, Research Scholar, Physical Oceanography Division, CSIR- National Institute of Oceanography contributed to the collection of data and processing of the raw data respectively. Mr. Mani Murali also contributed to the written work related to the methodology of PAR data collection and processing.
Acknowledgements
I would like to thank my Research Supervisor Dr. J. Ravindran, Senior Scientist, Biological Oceanography Division, National Institute of Oceanography for his help and guidance to complete this work. His suggestions, constant and sincere encouragement, insightful discussions and critical evaluation for improvement have been more helpful to complete my work within the stipulated time.
I acknowledge the award of INSPIRE fellowship to me by the Department of Science and Technology (DST), Government of India enabling me to register for PhD.
I’m grateful to Dr. S.W.A. Naqvi, Director, CSIR- National Institute of Oceanography for his encouragement and support. I want to especially thank him for being the external examiner for my JRF assessment and rendering valuable suggestions to improve my work. I also acknowledge his financial support for travel during my field trips.
This research involved tremendous amount of field work and it would not have been possible without the help of Mr. Kathiresan, Boat personnel in Mandapam. I gratefully acknowledge his constant support during my field observations and for other logistical supports in the field. I also thank Mr. K. Paramasivam and Mr. S.
Shrinivaasu, Research Scholars, Marine Biology Regional center, Zoological Survey of India for their assistance during the field works.
I would also like to express my thanks to Dr. Mohideen Wafar, Retired Scientist, National Institute of Oceanography, Goa for his valuable suggestions during the
course of my study; Dr. Rajkumar Rajan, Scientist-In- Charge, Marine Biology Regional Center, Zoological survey of India for his help in identification of corals;
Dr. E. Kannapiran, Professor, Department of Zoology, Directorate of Distance Education, Alagappa University, Karaikudi for his support and encouragement; Dr.
Vaibhav Ajit Mantri, Scientist-In-Charge , Marine Algal Research Station, Mandapam for rendering lab facilities and Dr. K. Jeyakumar, Assistant Professor, School of Biological Sciences, Madurai Kamaraj University for his constant encouragement and suggestions.
Ultimately, I am thankful to my Parents who supported me morally and financially throughout my PhD. I also thank all my friends and colleagues in National Institute of Oceanography, Regional Center, Kochi and Headquarters, Goa for their moral support, appreciation and encouragement.
B Manikandan
Contents
1. Chapter 1 – General Introduction ………..………...…… 01 - 12
1.1. Corals and coral reef ecosystems ………...…….….…….… 01
1.2. Changes in coral reef ecosystems and their implications …………...……... 03
1.3. What is Resilience? ………...….……….…….. 06
1.4. Need for a Resilience based management system ………....………..……... 06
1.5. Scientific knowledge on the corals of Indian reefs ………..………. 07
1.6. Research Problem addressed ………....………. 10
1.7. Major Objectives of the study ……….………...……… 12
2. Chapter 2 –Coral recruitment pattern and survival of juvenile corals amid recurrent stress events …………..……….………….. 13 - 44 2.1. Introduction ……….………..……….... 13
2.1.1. Coral recruitment and its contribution towards resilience ….………. 14
2.1.2. Factors affecting coral recruitment ………...…… 15
2.1.3. Recruitment failure and its implications in the reef ecosystem ...…. 17
2.2. Materials and Methods ……….………..………...…. 18
2.2.1. Study sites ……….….…………..…………..………… 18
2.2.2. Benthic composition ……….………..……...………. 20
2.2.3. Coral recruitment pattern ………..………….………. 20
2.2.4. Coral recruitment rate ………..………..………. 20
2.2.5. Survivability of juvenile corals ……….. 21
2.2.6. Environmental conditions during stress events …………..………… 22
2.2.7. Analysis ……….……….……… 23
2.3. Results ………...………. 24
2.3.1. Benthic composition ………..………. 24
2.3.2. Juvenile and Adult coral diversity ………...……….….. 25
2.3.3. Density and Taxonomic composition of juvenile corals ………... 27
2.3.4. Size structure of juvenile corals ………..………... 30
2.3.5. Recruitment rate of corals ………...………...…… 31
2.3.6. Survival and Mortality of juvenile corals ……….…………. 32
2.3.7. Environmental conditions during the stress events ……..….……… 36
2.4. Discussion ……….…..………….…. 37
.
3. Chapter 3 – Coral community dynamics ………...…... 45 - 68
3.1.Introduction ……….…...……… 45
3.1.1. What triggers macroalgae bloom? ……….. 46
3.1.2. Implications of macroalgae bloom in coral reef ecosystems ………. 47
3.2. Materials and Methods ……….…………..…………..………. 48
3.2.1. Study sites ……….…………..…………..………. 48
3.2.2. Photo sampling method ……….………..….………..………… 50
3.2.3. Analysis ……….………...………..………… 51
3.3. Results …..……….………..….. 52
3.3.1. Initial assessment ……… 52
3.3.2. Coral community dynamics at Vedhalai ……… 53
3.3.3. Coral community dynamics at Mandapam ……….……… 59
3.4. Discussion ………..……….….….…… 63
4. Chapter 4– Bleaching and recovery patterns of corals in Palk Bay.…... 69 - 89 4.1. Introduction ………..…….………….... 69
4.2. Materials and Methods ……….………….….………... 72
4.2.1. Study sites ……….………..………...… 72
4.2.2. Bleaching Survey method ………..……….... 73
4.2.3. Environmental conditions during bleaching ……….……...74
4.2.4. Analysis …...………....………75
4.3. Results ………..…….…… 76
4.3.1. Bleaching event 2013 ………..…….……….. 76
4.3.2. Bleaching event 2014 ………..….…..…… 79
4.3.3. Differential susceptibilities among corals of different genera …...… 83
4.4. Discussion ………...…….…. 84
5. Chapter 5- Reef fish stock, exploitation and its implications on the corals of Palk Bay ………...……… 90 - 120 5.1.Introduction ………..…………..… 90
5.2. Materials and Methods ……….……….…… 93
5.2.1. Study sites ……….………. 93
5.2.2. Reef fish survey ………. 95
5.2.3. Reef fish exploitation ……….... 96
5.2.4. Coral community assessment ……… 96
5.2.5. Analysis ……….………. 97
5.3. Results ………..…... 98
5.3.1. Reef fish diversity ………...……..… 98
5.3.2. Reef fish density ……….. 102
5.3.3. Reef fish exploitation ………... 105
5.3.4. Coral community structure ………... 107
5.3.5. Status of Live corals ………... 112
5.4. Discussion ………...….. 114
6. Chapter 6 – Final summary and Conclusion ……… 121 - 128 6.1. Current scenario of Palk Bay reef ………...……… 121
6.2. What factors drive the degradation of corals of Palk Bay? ……….122
6.3. Promising factors of resilience in Palk Bay reef ……….………… 124
6.4.Future research focus ……… 126
6.5. Strategy for enhancing the resilience potential of Palk Bay reef ……...…. 127
6.5.1. Monitoring ……… 127
6.5.2. Reef Management ……….………128 Literature cited ………...…………. 129 - 149 Appendix – List of Publications ……….……… 150 - 151
List of abbreviations
ANOSIM - Analysis of Similarity
ANOVA - Analysis of Variance
CCA - Crustose Coralline Algae
GoMBR - Gulf of Mannar Marine Biosphere Reserve GoMNP - Gulf of Mannar Marine National Park LIT - Line Intercept Transect Method
MODIS - Moderate Resolution Imaging Spectroradiometer
MPAs - Marine Protected Areas
NE monsoon - Northeast monsoon
PAR - Photosynthetically Active Radiation
PCA - Principal Component Analysis
PCoA - Principal Coordinate Analysis
ROS - Reactive Oxygen Species
SIMPER - Similarity Percentage
SST - Sea Surface Temperature
SW monsoon - Southwest monsoon
TSS - Total Suspended Solids
1 | P a g e
Chapter 1
General Introduction
1.1 Corals and Coral reef ecosystems
The coral reef ecosystems are the most ancient and dynamic ecosystems on the planet. They are biologically diverse and highly productive ecosystems (Odum and Odum 1955). In general, the term ‘Reef’ refers to the continuous underwater lime stone structures built by marine organisms. Scleractinian corals are the principal reef building organisms and form the reef frame work that serves as a habitat for numerous life-forms (Owen et al. 2012). Corals are the colonies of individual polyps which secrete an external calcium carbonate skeleton through the process of calcification (Smith 1983). The coral calcification process is driven by the symbiotic microalgae called zooxanthellae that reside within the coral tissues. The corals are classified as hermatypic and ahermatypic corals based on their ability to secrete calcium carbonate skeleton and build reefs. Hermatypic corals host zooxanthellae, secrete calcium carbonate skeleton and build reefs. Ahermatypic corals are azooxanthellate species and do not build reefs (Marshall 1996). The other reef building organisms include crustose coralline algae (CCA), encrusting algae and calcareous algae all of which secrete hard calcium carbonate and contribute to the reef growth (Castro and Huber 2003). In addition, sponges, octocorals and other invertebrates also contribute to the process of reef formation.
Since corals are the primary reef building organisms, their growth requirements limit the distribution of reefs. Coral reefs are predominantly present along the tropical coast lines between the latitudes 30 °N - 30 °S which constitute half
2 | P a g e of the world’s coast lines (Spalding et al. 2001). The distribution of corals is influenced by various factors including temperature, light availability, sediment load, substrate type, depth and turbulence, all of which may act independently or synergistically to prevent or promote the reef growth (Veron 2000). The upper temperature limit for the growth of corals is 30 °C, although certain corals can withstand temperatures up to 35 °C. Cold water corals which are found globally at the depths >70 m from the coastal Antartica to Artic circle can thrive at a temperature of 4 °C. Corals thrive well in the shallow, clear waters with maximum light penetration since light is essential for photosynthesis by their symbiotic partner zooxanthellae.
Coral reefs cover <0.5% of the ocean floor (Lough 2008) and serves as home to 25% of the known marine population. Coral reefs provide numerous economical, ecological, biotic and biogeochemical services that benefit the people living along the tropical coastlines and also contribute to the ocean processes. Healthy coral reefs are a source of food for millions; protect coastlines from waves, storms and erosion;
provide habitat for other organisms, spawning and nursery grounds for economically important fish species; provide jobs and income to local people from fishing, recreation, and tourism; source of new medicines, and are hotspots of marine biodiversity (Cesar 2003, Moberg and Folke 1999). The standing stock of fishes in the coral reefs comprises a significant portion of the total fish stock in the world ocean (Sorokin 1993, McAllister 1994). A healthy coral reef of 1 km2 can support over 300 people in the absence of other protein sources (Jennings and Polunin 1996). The export of organic matter and combined nitrogen from coral reefs contributes to the productivity of Ocean. Coral reefs forms Islands facilitating the settlement of human population (Stoddart 1973); promote the growth of seagrass and mangrove ecosystems by dissipating the wave energy and creating lagoon and sedimentary
3 | P a g e environment (Birkeland 1985, Ogden 1988); serve as a breeding, feeding and spawning ground for multiple organisms thereby maintaining the immense biological diversity. The role of coral reefs as nitrogen fixers (Sorokin 1993) contribute to the productivity of adjacent pelagic communities due to the release of excess nitrogen fixed in the reef ecosystem (D’Elia 1988, Sorokin 1990).
1.2 Changes in coral reef ecosystems and their implications
Coral reef ecosystems are highly dynamic and extremely sensitive to the fluctuations in their environmental conditions. Despite their services, the coral reef ecosystems are under continuous degradation globally due to human induced climate change and environmental pollution (IPCC 2001, Wilkinson 2008, Riegl et al. 2012).
The rate of degradation of corals was high enough to thrust the corals to the risk of extinction (Carpenter et al. 2008). The carbon dioxide and temperature levels are projected to exceed their threshold limit to corals pushing them to extreme conditions which they had never experienced before (Hughes et al. 2003). The climate change exert its impacts through variety of processes including warming seas, ocean acidification, diseases, altered currents, strong storms and rising seas. All these processes are capable of degrading corals by inducing physiological stress response and mechanical damage. Loss of corals will result in trophic cascades and turns a coral dominant reef in to an algal dominant reef losing its aesthetic values and functions.
The ever increasing Sea Surface Temperature (SST) disrupts the coral-algal symbiosis resulting in coral bleaching (Brown 1996). Corals, the major reef building organisms are the visible bio-indicators alarming the rise in SST. The major bleaching event that occurred in 1998 significantly reduced the live coral cover up to 50%
globally (Wilkinson 2000). Since then, the frequency of bleaching events increased
4 | P a g e though they were less severe compared to the 1998 event and become a common phenomenon globally, reducing the live coral cover in most of the reefs (Spencer et al.
2000, Marshall and Baird 2000, Arthur 2000, McClanahan 2007a). Coral bleaching leads to severe ecological implications including coral mortality, reduced coral growth, changes in community structure, decrease in species diversity and decrease in reef fish assemblage (Booth and Beretta 2002, Bellwood et al. 2006a, Baird and Marshall 2002, Glynn 1996, Ostrander et al. 2000). In addition, coral bleaching also weakens the reef frame work and results in the loss of critical habitats for the reef fishes (Baker et al. 2008).
The uptake of CO2 by the ocean reduced the pH of the seawater and it influences the biological systems in the ocean. Changes in pH of the ocean compromise the role of corals as the primary reef building organisms by affecting the coral growth and calcification process making them more vulnerable to natural stress (Feeley et al. 2004). The growth of corals and other calcifying organisms has to be at pace with the erosion failing which the ocean acidification process will lead to loss of corals by eroding their skeleton thereby weakening the reef frame work. In addition, high CO2 induces bleaching in corals and also decrease their productivity (Anthony et al. 2008).
Coral diseases linked to climate change are often difficult to predict as several factors are involved in inducing the outbreak of diseases (Bourne et al. 2009, Ainsworth et al. 2010). Transport of Aeolian dust from Saharan Africa is considered to be the outcome of climate change and hypothesized to cause coral disease in Caribbean reefs (Shinn et al. 2000). The Sea level rise linked to climate change is not a major threat to corals as the projected rates of increase in sea level is low enough to keep the fast growing corals at pace (Knowlton 2001). However, the existence of slow
5 | P a g e growing corals is at risk (Hoegh-Guldberg 1999). The frequency and severity of tropical storms is expected to increase in future. Gardner et al. (2005) reported that the Caribbean corals require at least 8 years to recover from the damage incurred by the storms. Increase in the frequency of the storms will reduce the time available for the corals to recover. The other impacts of climate change include changes in species composition, primary and secondary production, diversity and community structure (Harley et al. 2006).
Unlike climatic stressors which evoke a chronic response among corals, human activities inside a coral reef ecosystem evoke a quick lethal response among the coral population. Continuous increase in the coastal population along the tropics increased the risk to reefs in the form of sedimentation, pollution, coastal development and over exploitation of reef resources (Wilkinson 1999). Collectively, all these activities lead to the degradation of corals which will have profound implications over the entire reef ecosystem (Hodgson 1999, Halpern et al. 2008). The human induced threats have weakened the recovery potential of corals from natural stress leading to their mortality and permanent loss (Ravindran et al. 2012). The reefs that occur adjacent to the land are severely affected by sedimentation (Dubinsky and Stambler 1996).
In shallow reefs there is a continuous re-suspension of sediments due to currents and tidal fluctuations which allows the sediment to settle on corals. This reduces the light available to corals for performing photosynthesis and depletes the energy stock of corals (Bryant et al. 1998). Organic and Inorganic pollution leads to nutrient enrichment in reefs that encourage algal population and bio-erosion thereby weakening the reef frame work (Glynn 1997). The impacts of nutrient enrichment are exaggerated with fishing pressure. Increased fishing pressure results in reduced
6 | P a g e herbivory which in turn promotes the algal growth in a coral dominated ecosystem.
The macroalgae possess the potential to prevent the recovery of corals post a stress event like bleaching; kill the corals by secreting toxic metabolites (Rasher et al.
2011); trap the sediments and prevent the settlement of new coral colonies (Birrell et al. 2005).
1.3 What is Resilience?
The term Resilience refers to the ability of a system to absorb the recurrent stress and adapt to it without changing to an alternate stable state and maintain its functions (Hughes et al. 2010). Several factors including live coral cover and diversity, herbivore fish biomass, coral recruitment, Ecosystem connectivity etc plays a critical role in strengthening the resilience potential of the coral reef ecosystems (McClanahan et al. 2012). Whereas, other factors like over exploitation of reef resources, frequent community phase shifts, increase in the frequency of natural threats, development of coastal areas adjacent to the reef and poor management of the reefs will weaken the resilience potential of the coral reef ecosystems.
1.4 Need for a Resilience based Management System
The coral reef ecosystems can recover to their normal state post a stress event provided with favorable conditions and no further disturbances from other sources.
The recovery of corals post a stress event depends on numerous factors including food availability (Connolly et al. 2012), reef characteristics, reef connectivity, reduced anthropogenic stress (Graham et al. 2011), effective management through Marine Protected areas (MPAs) (Mumby and Harborne2010) and a healthy stock of herbivore fish population (Mumby et al. 2007). In addition to recovery, the corals have evolved adaptive strategies to withstand the stress generated by the processes of climate change (Berkelmans 2006). Corals mitigate the thermal stress through adaptive
7 | P a g e processes including symbiont shuffling (Rowan 2004, Kinzie et al. 2001), acclimatization and genetic adaptation (Coles and Brown 2003). Corals also possess internal mechanisms to adapt ocean acidification by up regulating the pH at their site of calcification (McCulloch et al. 2012). The impacts of climate change processes are exacerbated when combined with the impacts generated by local scale regional stressors. No adaptive mechanisms have been described to be possessed by corals against human induced local threats.
Majority of the studies describing the impacts of climate change and environmental stress deal with individual level changes in response to a single factor (Hughes et al. 2003, Harley et al. 2006). Under natural conditions, two or more factors interact and act synergistically to drive the organism beyond their threshold limit. It is important to address the synergistic effect of climatic and environmental factor as the effect of one factor can either strengthen or dilute the effect of other factor. MPAs offer protection to the reefs at different scales from human induced threats. However, the profound activities of humans inside the reef ecosystem and poor execution of the management practices have diluted the potential of MPAs from protecting the reefs. The coral ecosystems can be managed by regulating the human activities inside it. However, such regulations cannot prevent the changing climate or warming seas from taking toll over corals. A resilience based management strategy is essential to minimize the impacts generated by the climatic processes thereby to facilitate and enhance the natural recovery of corals post a disturbance event.
1.5 Scientific Knowledge on the corals of Indian Reefs
India has a vast coast line that extends up to 8000 km. Coral reefs occur along the Gulf of Kachchh and Lakshadweep archipelago on the west coast and Gulf of Mannar(GoM) & Palk Bay and Andaman & Nicobar Islands in the east coast (Vineeta
8 | P a g e Hoon 1998) (Fig 1.1). Lakshadweep reefs are coral atolls whereas the other reefs are of fringing and barrier reefs. Small patchy reefs occur along the central western coast of India between Maharastra and Goa (Venkataraman et al. 2003). Andaman &
Nicobar Islands in the Bay of Bengal and Lakshadweep Islands in the Arabian Sea are the major reef formations in India encompassing a reef flat area of 795.7 km2 and 136.5 km2 respectively. Coral reefs are estimated to cover an approximate area of 2375 km2 in India (Venkataraman 2007).
The Palk Bay reef in the southeast coast of India is the study area chosen for this study. It occurs between the Latitude 9°55’-10°45’N and Longitude 78°58’- 79°55’E. The Palk Bay reef is of fringing type located 200-500 m away from the shore. The reef is discontinuous and extends about 7 km towards the north eastern side of Mandapam peninsula. In total, 63 species of corals belonging to 23 genera were reported earlier in Palk Bay with variety of flora and fauna associated with it (Pillai 1969). The diversity and distribution of corals and other associated fauna in Palk Bay has been well documented (Mahadevan and Nayar 1972, Pillai 1969, Rao 1972). Few studies have addressed the impacts of Tsunami and bleaching on the corals of Palk Bay (Kumaraguru et al. 2005, Kumaraguru et al. 2003, Arthur 2000).
However, the profound impacts of human activities and climatic factors at individual and at community level within the reef ecosystems of Palk Bay have not been addressed.
The corals in Palk Bay are strongly influenced by both the climatic and anthropogenic factors apart from the other biological agents. The Northeast (NE) monsoonal winds stir up sediments from the substrate increasing the amount of sediment settling on corals. This had reduced the live coral cover in Palk Bay and restricted the species diversity of corals to massive forms with large polyps which are
9 | P a g e capable of removing the sediments settling on them (Pillai 1975). Tropical cyclone that occurred in 1964 incurred severe mechanical damage to corals and reduced the live coral cover in Palk Bay (Pillai 1975). Increase in SST during summer results in Coral bleaching. Three major bleaching events were reported in Palk Bay reef which significantly reduced the live coral cover (Arthur 2000, Pet-Soede et al. 2000, Kumaraguru et al. 2003, Ravindran et al. 2012).
Sedimentation linked to the monsoonal patterns and tidal flux is the major factor affecting the corals in Palk Bay (Wilson 2005). Anthropogenic influences such as high fishing pressure, pollution, mechanical damage and high sedimentation have largely contributed to coral degradation in Palk Bay. Palk Bay reef was a potential fishing ground for small-scale fishermen throughout the year except during the period of NE monsoon that falls between October to December every year. The peak fishing season in Palk Bay is between January to September and the fishing effort ranges between 30 days boat-1 in the intensive reef fishing sites and 15±4 days boat-1 in lightly fished reef sites. The existing reef fishing practices in Palk Bay include deploying underwater cages, shore seine, trap nets, bait fishing and throw nets (Kumaraguru et al. 2008 ). Of these practices, trap net fishing and cage fishing incur mechanical damage to the corals affecting their structural complexity and these two practices are followed by majority of the fishermen in Palk Bay.
The biological agents that pose threat to the corals of Palk Bay include the predators and borers. While the predators feed directly on the coral polyps, the borers lead to the erosion of individual coral colonies (Ormond et al 1973). The borers include sponges, polychaetes, barnacles, bivalves and molluscs. Two species of polychaetes (Pillai 1975), 20 species of sponges (Thomas 1972) and 17 species of bivalves (Appukuttan 1972) were reported to be the common coral borers in Palk Bay.
10 | P a g e 1.6 Research Problem addressed
The Palk Bay reef in the Southeast coast of India is influenced by both climatic as well human activities to larger extent. The Gulf of Mannar Marine Biosphere Reserve (GoMBR) encompasses both Palk Bay and Gulf of Mannar (GoM). However, the Palk Bay was less protected compared to the adjacent GoM despite its biological significance and species richness. The corals in Palk Bay are highly influenced by bleaching, monsoonal pattern and sedimentation (Kumaraguru et al. 2003, Ravindran et al. 2012, Wilson et al. 2005). Human pressure in the form of reef fish exploitation, careless boat operations and pollution linked with the climatic factors such as thermal stress, monsoonal pattern and sedimentation and contribute to the degradation of corals in Palk Bay. The level of degradation of corals and the factors driving it are the critical problems that have obvious implications in formulating policy and improving the management of these ecosystems. Moreover, the 1998 bleaching event significantly reduced the live coral cover in Palk Bay.
Thereafter two other major bleaching events were reported in 2002 and 2010 (Kumaraguru et al. 2003, Ravindran et al. 2012). There are no systematic studies that have quantified the recovery of corals and its resilience in Palk Bay post the bleaching events.
In the proposed study, I attempt to characterize the trend of those factors that influence the resilience potential of the Palk Bay reef. The resilience potential of a reef depends on numerous factors including coral recruitment, herbivore fish population, community-phase shifts, ecosystem connectivity and effective management. Knowledge on the trend of those factors that influence the resilience potential of a coral reef ecosystem of concern is essential, as it can help managers to avoid ecosystem catastrophes by devising a resilience based management strategy. At
11 | P a g e present there is no resilience based management system governing the Palk Bay. It is important to devise a local management strategy that focuses on the fisheries management, limitations of terrestrial input and offering protection to the core and adjacent ecosystems (Adam et al. 2011).
Fig 1.1. Map showing the distribution of coral reefs in India.
12 | P a g e 1.7 Major Objectives of the Study
To determine the rate and recruitment pattern of corals and the survival rate of new recruits in Palk Bay.
To determine the community dynamics and their impacts on the coral ecosystems of Palk Bay.
To determine the bleaching and recovery patterns among the corals of Palk Bay.
To determine the standing stock of reef fish and exploitation and its impact on coral ecosystem of Palk Bay.
13 | P a g e
Chapter 2
Coral recruitment pattern and survival of juvenile corals amid recurrent stress events
2.1. INTRODUCTION
Continuing degradation of global coral reefs warrant the need for a resilience based management of coral reef ecosystems which in turn require the evaluation of key factors that contribute to the recovery and resilience of a degraded reef. Corals are the primary reef building organisms and loss of corals deprives the functional and economic values of the reef affecting the reef dependents. The 1998 bleaching event degraded and reduced the live coral cover up to 50% worldwide (Wilkinson 2000).
The Caribbean reefs are largely degraded due to hurricanes, overfishing and diseases and the live coral cover was reduced up to 90% (Hughes 1994). In Southeast Asia, the human activities including destructive fishing, overfishing, pollution, diseases and sedimentation from inland sources had largely contributed to the degradation of corals (Burke et al. 2006). Community shift towards an algal dominated state due to poor water quality and increased human pressure degraded the Florida reefs (Porter et al.
2002). Large scale mortality of corals in response to any stress event often leads to the replacement of corals with macroalgae or other benthic organisms (Bak et al. 1984, Alvarado et al. 2004, Norstorm et al. 2009). In order for these reefs to recover to a coral dominated state, an adequate supply of coral larvae from other pristine reefs
14 | P a g e were required that are able to settle and grow successfully resisting the stress conditions.
2.1.1. Coral recruitment and its contribution towards resilience
The worldwide degradation of corals underscores the need for an effective resilience based management system which in turn emphasizes the need for identifying the key resilience indicators in a reef ecosystem. Coral recruitment is one among the key resilience indicators that determines the health of a reef and helps in the development of a policy for an effective reef management (McClanahan et al.
2012, West and Salm 2003). In general, coral recruitment is defined as the successful settlement of the coral larvae over any hard substrate and attaining a size visible to a naked eye by growth (Moulding 2005). The sexual reproduction of corals and the ensuing larval dispersal enabled the corals to distribute their off-springs over a wide geographic area contributing to the replenishment of a degraded coral reef ecosystem.
Recovery of a coral population in a degraded reef post a stress event like bleaching, storm & cyclones and algal blooms depends on numerous factors including the regeneration of the affected colonies, self-seeding of the reef by the surviving colonies and supply of coral larvae from distant reefs (Obura 2005, Gilmour et al.
2013). High coral recruitment rate enables a reef to be coral dominant and the surviving recruits serve as the seeds for a degraded reef within few years of their settlement (Obura 2005). When the coral recruitment rates were high, the reef can recover quickly despite the type and severity of the disturbance event (Graham et al.
2011). Under reduced fishing pressure, successful settlement and recruitment of coral larvae has the potential to reverse an algal dominated reef in to a coral dominated reef (Elmhirst et al. 2009). Anthropogenic intervention has no significant impact on the
15 | P a g e recruitment of corals which in turn leads to the recovery of an anthropogenically disturbed reef (Sawall et al. 2013).
2.1.2. Factors affecting coral recruitment
The recovery potential of a degraded reef becomes undermined when the recruitment of new coral colonies becomes inadequate. Availability of coral larvae, their successful settlement and post settlement survivability are the three critical factors determining the recovery and maintenance of the degraded coral reef ecosystems (Ritson-Williams et al. 2009). Several stressors including poor water quality, human intervention, predation and climatic conditions influenced the coral larvae in different stages of their life history. Ocean acidification reduced the availability of Crustose Coralline Algae (CCA) which in turn reduced the coral larval settlement and their settlement behavior (Doropoulos et al. 2012). Experimental evidences indicate that Ocean acidification has the potential to reduce the fertilization rate and settlement success of coral larvae (Albright et al. 2010). Similarly coral bleaching which occurs as a result of elevated temperature and radiation has the potential to reduce the reproductive output of the corals (Baird and Marshall 2002).
The abundance and diversity of fishes in a coral reef ecosystem serves many purpose including creating substrates for coral recruitment by grazing the turf algae.
Removal of reef fishes from the coral reef ecosystem influence the recruitment pattern of corals by enabling the proliferation of macroalgae over the available hard substrates. This in turn poses stiff competition to corals for space and prevents the settlement of new coral recruits (Kuffner et al. 2006). Similarly removal of predatory fishes, affected coral recruitment by producing a sea urchin dominated grazing community which in turn reduced the CCA cover (O’Leary et al. 2012). CCA induce the settlement of coral larvae by producing chemical signals (Heyward and Negri
16 | P a g e 1999). However, only few species of CCA facilitate the settlement of coral larvae and many other species of CCA possess anti settlement defence mechanism (Harrington et al. 2004). In Jamaican reefs, recovery of the herbivory sea urchin Diadema sp had promoted the density of new coral recruits (Carpenter and Edmunds 2006).
Macroalgae bloom which primarily occurs due to reduced herbivory, nutrient enrichment and wide spread coral mortality prevents the settlement and recruitment of new coral colonies by competing for space (Hughes 1994, Szmant 2002, Kuffner et al.
2006). Coral reef ecosystems with high macroalgae cover coupled with less coral recruitment and low growth rate of corals were extremely vulnerable to the disturbances generated by the processes of climate change (Hoey et al. 2011).
Macroalgae kills corals and new coral recruits directly in variety of ways including smothering, mediating pathogens and secreting allelophobic chemicals (Rasher et al.
2011). Other than macroalgae, the turf algae in association with sediment inhibit the settlement of coral larvae (Arnold et al. 2010, Birrell et al. 2005).
In general, the density of new coral recruits was low in the areas with high sedimentation (Edmunds and Gray 2014, Trapon et al. 2013). Though high level of sedimentation has no impact on the gamete development or fecundity (Padillo- Gamina et al. 2014), it is known to reduce the level of fertilization success by preventing the settlement of coral larvae (Perez et al. 2014, Erftemeijer et al. 2012).
Other natural stressors like cyclones will result in the loss of entire colony or patches of tissue within a coral colony which in turn compromise their sexual fecundity (Williams et al. 2008). Creating marine reserves and effective enforcement of laws minimized the human intervention inside the marine reserves and increased the density of new coral recruits which in turn promoted the resilience potential of the reef (Mumby et al. 2007).
17 | P a g e 2.1.3. Recruitment failure and its implications in the reef ecosystem
The inability of a degraded reef to regain their coral population and subsequently recover to a coral dominated state is largely due to the changes in the fecundity, fertilization success, larval dispersal and recruitment. Failure of any of the above process promotes shift in the community composition of corals and reduction in the live coral cover (Hughes et al. 2010). Coral recruitment failure leads to a lack of growth or retarded recovery of reefs in case of degradation and causes local extinction of species post a disturbance event (Hughes and Tanner 2000). Loss of corals also weaken the reef structure making it more vulnerable to the natural stressors like cyclones, wave action etc. and eliminate the important micro habitats available for fishes (Glynn 1997).
In addition to adequate supply of coral larvae and high recruitment rate, the survivability of the juvenile corals in response to the prevailing stress conditions in the recipient reef also plays a critical role in determining the resilience potential of a reef. The Palk Bay reef located in the southeast coast of India was largely affected by the 1998 bleaching event. Thereafter, two other massive bleaching events reported in 2002 and 2010 in the reef (Kumaraguru et al. 2003, Ravindran et al. 2012).
Collectively, these events reduced the live coral cover, diversity and density of the corals in the reef. Recovery and resilience of the Palk Bay reef is not known as there were no systematic studies carried out in those lines. Live coral cover is a simple and powerful parameter to evaluate the status and health of a reef. Increase in the live coral cover is determined by the growth of the existing live corals and/or addition and growth of new recruits. Any process that alters the live coral cover indicates the reduction in the health of a reef and denotes their degradation. So, these parameters can be used to determine the resilience potential of a reef. The major goals under this
18 | P a g e objective was to assess the live coral cover, its diversity and recruitment pattern of juvenile corals as an indicator for determining the potential recovery and resilience of the coral reef assemblages in the Palk Bay reef through monitoring over a period of two years. Three spatially distant reefs were selected along Palk Bay which is influenced by the human activities at different levels. The specific goals of this objective include (i) to assess the live coral cover, its diversity and coral recruitment pattern (defined by the diversity, density, size structure and taxonomic composition of the juvenile corals) (ii) to determine the annual coral recruitment rate over the natural substrates such as dead coral skeleton and CCA and (iii) to assess the survivability of the juvenile corals during the observation period in response to the prevailing stress conditions in Palk Bay. This assessment will contribute in the management plan for the conservation of Palk Bay reef.
2.2. MATERIALS AND METHODS 2.2.1. Study sites
The study was carried out at three spatially distant reefs (Vedhalai, Mandapam and Pamban) along the Palk Bay named on the basis of their near shore locations and influenced by different scales of human activities (Fig 2.1). The human activities including reef fishing, drifting of boats, trawl boat passage, boat cleaning and shore seine operations were moderate in Vedhalai; high in Mandapam and low in Pamban reefs (Table 1). Two study sites were selected in each reef and observed for the live coral cover, rate and recruitment pattern of corals and survivorship of juvenile corals in response to the stress conditions prevailing in Palk Bay. The juvenile corals were identified to the genus level. In addition, diversity of adult coral colonies at the study sites was recorded to know whether the Palk Bay reef is self seeded or connected with
19 | P a g e other reefs. Species level identification of juvenile corals and adult coral colonies was not possible due to the legal restrictions in the collection of coral samples in India.
Fig 2.1. Map showing the location of the study sites observed for coral recruitment pattern and survivorship of juvenile corals at Palk Bay reef. V1 & V2 – Vedhalai; M1
& M2 – Mandapam; P1 & P2 – Pamban.
Table 1- Human activities and types of disturbances at the study locations along the Palk Bay reef.
Location Disturbance level Types of disturbances
Vedhalai Moderate Reef fishing; Drifting boats over corals;
seaweeds culturing
Mandapam Severe Reef fishing, boat drifting; trawl boat operations; boat cleaning; sewage discharge; shore seine operations; trap net fishing
Pamban Low Reef fishing
20 | P a g e 2.2.2. Benthic composition
The percent cover of live corals and other benthic components including dead corals, macroalgae, rubbles and sand were estimated following the Line Intercept Transect (LIT) method (English et al. 1997). Four 20 m transects were established, two parallel to the shore and other two perpendicular to the shore at each study site.
Benthic forms that falls under the transect were recorded and their average percent cover was calculated.
2.2.3. Coral recruitment pattern
A modified belt-transect method (English et al. 1997) with a swath of 5 m was employed to study the recruitment pattern of the juvenile corals at the study sites.
Corals of the size ≤5 cm in diameter was considered for this study as it translates into both recruitment a well the urviva ility for 2yrs with a presumed growth rate of 1-3 mm diameter every month (Moulding 2005, Bak and Engel 1979). In total, four 20 m transects were laid, two parallel and two perpendicular to the shore at each study site.
All the juvenile corals that fall within the effective width of the transect were enumerated, measured to their nearest size (mm) and identified at genus level (Veron 2000). The average density was expressed as a number of coral juveniles m-2 averaged over all the four transects at each study site. The taxonomic composition was calculated as the percentage of juveniles in each genus relative to the total number of juveniles in the other genera. The diversity of adult coral colonies was determined on the same transects surveyed for juvenile corals.
2.2.4. Coral recruitment rate
The recruitment rate of corals was assessed over the natural substrates such as dead coral skeleton and CCA following the permanent quadrat method (English et al.
1997). The standard method of deploying artificial substrates such as tiles was not
21 | P a g e employed, as it will not reflect the actual scenario. Moreover, the size of the juveniles of ≤5 cm which helped in this approach for the underwater observation. An area of 1 m2 size comprising hard substratum such as dead coral skeleton, CCA etc. was demarcated using a portable quadrat and fixed in permanence. In total, 10 quadrats were established in each site and each quadrat was placed atleast 5 m apart during September 2012. The quadrats were thoroughly examined visually and also digitally using a high resolution underwater photography to create a baseline on the presence of juvenile corals. The quadrats were re-examined similar way in September 2014 for the presence of any juveniles. The juveniles within each quadrat were enumerated and pooled across the quadrats in each study site and reported as a number of juvenile corals 10 m-2 2 years-1.
2.2.5. Survivability of juvenile corals
The juvenile corals were tagged initially in September 2013 before the commencement of Northeast (NE) monsoon that usually occurs between October to December every year and the seawater remains turbid till March of the next year due to high level of suspended sediments. A total of 100 juveniles were tagged by nailing the numbered poly propylene tags at each study site to study their survival rate in response to the NE monsoon associated sedimentation stress. The tagged juveniles were visually and digitally observed post NE monsoon during April 2014 to estimate their survivability. The survivability was assessed by visually estimating the number of juveniles that were alive, dead and partially dead relative to the total number of juveniles that were tagged alive before the NE monsoon. Similarly, juveniles were tagged during March 2014 and thereafter monitored every month at regular intervals till September 2014 for their vulnerability to bleaching and related mortality.
22 | P a g e Vulnerability is calculated as the percentage of juveniles that were bleached and remained unresponsive to bleaching relative to the total number of juveniles tagged.
2.2.6. Environmental conditions during stress events
The Palk Bay reef is influenced by both Southwest (SW) and NE monsoon.
During NE monsoon, the wind generated waves stir up the bottom sediments and leave them in suspension thereby increasing the level of suspended sediments in the water column and the rate of sedimentation over corals. It is not possible to determine the rate of sedimentation by deploying sediment traps due to high wave action and poor visibility. Hence the amount of total suspended solids (TSS mg/l) in the water column was measured during the NE monsoon period (Oct 13 - Jan 14). In addition, TSS was also measured during the pre NE monsoon (Jun 13 – Sep 13) and post NE monsoon period (Feb 14 – May 14) to know the level of variation in the amount of TSS during different seasons.
Data on sea surface temperature (SST) was obtained from a daily 9 km optimum interpolated global SST (MODIS+TMI) dataset for the period of March 2014- August 2014 (www.misst.org). The data was a merged product of both day and night in the Infrared and microwave wavelengths. From those data, average SST for every eight days was calculated and plotted. Photosynthetically Active Radiation (PAR) data at the ocean surface with a spatial resolution of 4 km was obtained from Moderate Resolution Imaging Spectroradiometer (MODIS) satellite. Similar to SST, the PAR values averaged for every 8 days was obtained for the period of March to September in 2014. The data was downloaded from the website (http://oceandata.sci.gsfc.nasa.gov). MODIS-Aqua satellite has ocean bands 8, 9, 10, 11, 12, 13, 14 in the visible range and the PAR values are estimated using these bands with specific algorithms (Frouin 2002). Data was flagged off for few days within the
23 | P a g e study period due to its poor quality. The accuracy of PAR data from MODIS-Aqua has average errors in the order of 5-8%, with individual estimation errors as high as 21% (Van Laake and Sanchez-Azofeifa 2005). This PAR data was used, as the high resolution PAR measurements are not available in this region. Since the sampling depth is around 2 m in clear waters, the PAR value on the surface may not change significantly during the downwelling. This PAR value must be giving representative information on the available light as the conditions remain same in the water column.
2.2.7. Analysis
Analysis of the data included the comparison of diversity, density and taxonomic composition of juveniles across the study sites. Shannon diversity Index (H’) and Pielou’ evenne index (J’) wa calculated for oth juvenile coral and adult coral colonies and compared. One-way Analysis of Variance (ANOVA) was used to test the significance of differences in the density of juveniles between the study sites in Palk Bay. The data on the density of juveniles at each study site has been log transformed to meet the assumptions of ANOVA including normality and homogeneity of variance. K-dominance curve was plotted for generic richness of the juveniles at the study sites where the different genera of the juvenile corals were ranked in their decreasing order of abundance. The relationship between the generic richness of the juveniles and adult coral colonies were analysed by calculating the correlations between the abundance of the juvenile corals and adults.
The study sites at Vedhalai, Mandapam and Pamban were segregated based on the taxonomic composition of the juveniles using Bray-Curtis similarity analysis under paired linkage. The data was fourth root transformed before the analysis.
Analysis of Similarity (ANOSIM) was used to test the significance of differences in the taxonomic composition of juveniles between the study sites. Similarity percentage
24 | P a g e (SIMPER) analysis was used to determine the contribution of each individual genus to the observed differences in generic composition between the study sites. All the analysis was performed using the PRIMER statistical software version 6.1.15 based on Warwick and Clarke (1991) and Clarke (1993).
2.3. RESULTS
2.3.1. Benthic composition
The average live coral cover along the Palk Bay reef was 8.25% and it was high in Vedhalai and low in Mandapam. The average live coral cover at the study sites varied between a minimum of 0.5% ± 7.7 (M2) to a maximum of 12.8% ± 4.5 (V1). The macroalgal cover was lower than the live coral cover at Vedhalai and Pamban and higher at Mandapam. Overall, macroalgae accounted for an average cover of 19.01% in Palk Bay and varied between a maximum of 27.9% ± 8.8 (V2) to a minimum of 2.1% ± 16.9 (V1) at the study sites. CCA were abundant in Mandapam and low in Vedhalai and Pamban. Also, the percent cover of Sand & Rubbles was several times higher in Mandapam compared to Vedhalai and Pamban. Average dead coral cover at Palk Bay was 27.4% and it varied among the study sites between 43.2%
± 15.8 (V1) to 8.3% ± 19.1 (M2). The percent cover of different benthic forms at the study sites of Palk Bay was summarized in the Fig 2.2.
25 | P a g e Fig 2.2. Average percent cover of different benthic forms at the study sites of Palk Bay. LC- live corals; DCA- dead corals with algae; MA- macroalgae; CCA- crustose coralline algae.
2.3.2. Juvenile and Adult coral diversity
The diversity of both juvenile and adult coral colonies were high in Pamban followed by Vedhalai and Mandapam. In total, 97 juveniles of 6 genera; 102 juveniles of 5 genera and 118 juveniles of 10 genera were recorded fromthe transects established at the study sites of Vedhalai, Mandapam and Pamban respectively. The mean generic richness of the juvenile corals across the study sites varied between a maximum of 10 genera (P2) to a minimum of 3 genera (M1). The corresponding Shannon diver ity index (H’, loge based) was typically high in P2 (2.03±0.75) (Mean
± SD) and low in M1 (0.48±0.8) and the juveniles of different genera were more evenly distributed in P1 (0.87) and P2 (0.88) followed V2 (0.83) (Fig 2.3a). Juvenile corals of the genus Leptastrea, Favia, Favites and Porites were prevalent in all the
0 20 40 60 80 100
V1 V2 M1 M2 P1 P2
Avg Percentage (%)
Study sites
LC DCA MA Sand Rubble CCA
26 | P a g e study sites. Other juveniles of Acropora, Goniastrea, Galaxea and Hydnophora were present only at the study sites of Pamban and absent at Vedhalai and Mandapam. The study sites at Vedhalai and Mandapam were largely dominated by the juveniles of Porites and Leptastrea sp whereas the study sites at Pamban was dominated byjuveniles of Goniastrea and Acropora sp.
Fig 2.3. Shannon diver ity index (H’) and Pielou’ evenne index (J’) of the juvenile corals (2.3a) and adult coral colonies (2.3b) at the study sites of Palk Bay. Error bars indicate standard error.
27 | P a g e Similar to juveniles, the diversity of adult coral colonies was high in the Pamban followed by Vedhalai and Mandapam. In total, 166 colonies of 7 genera; 35 colonies of 6 genera and 167 colonies of 12 genera were recorded fromthe transects established at the study sites of Vedhalai, Mandapam and Pamban respectively. The mean generic richness of the adult colonies varied between a minimum of 3 genera (M1) to a maximum of 12 genera (P2) and it showed a weak positive correlation with the diversity of juveniles corals (r= 0.59). The diversity index of adult colonies was high in P1 (2.055±0.4) and low in M1 (1.061±0.59) and adult colonies of different genera were more evenly distributed in P2 (0.91) and P1 (0.89) (Fig 2.3b). The highest generic diversity of the juveniles and adult coral colonies was evident in P2 and P1 as per the cumulative percentage of dominance of different genus ranked on the logarithmic scale (Fig 2.4a & 2.4b). However, the variation in generic richness of the juveniles (One-way ANOVA, F= 0.79; Fcrit= 2.38; p value = 0.58>0.05) and adult colonies (One-way ANOVA, F= 1.6; Fcrit= 2.31; p value = 0.15>0.05) was not statistically significant between the study sites.
Fig 2.4. K-dominance curve showing the variation in the generic richness of juvenile corals (2.4a) and adult coral colonies (2.4b).
2.3.3. Density and Taxonomic composition of juvenile corals
Mean density of the juvenile corals was high in Pamban (5.35 recruits m-2) followed by Mandapam (2.83 recruits m-2) and Vedhalai (2.34 recruits m-2). The
28 | P a g e average density of the juveniles differed significantly between the study sites (One- way ANOVA, F=6.07; Fcrit= 2.25; p value = 0.00005<0.05) and it varied between a maximum of 6.2 ± 2.1 m-2 (P1) to a minimum of 1.4 ± 2.75 m-2 (M1) (Fig 2.5).
Leptastrea and Porites sp were the most dominant genera contributing >90% to the total generic composition of the juveniles at the study sites V1 and M1 and >70% at V2 and M2. Goniastrea sp was dominant at P1 and P2 contributing >32% to the total generic composition. Juveniles of the Galaxea and Hydnophora sp were present only at P2 and each of these genera contribute <2.5% to total generic composition of the juveniles (Table 2).
Fig 2.5. Average density of juvenile corals across the study sites of Palk Bay. Error bars indicate standard error.
Table 2- Taxonomic composition (%) of juvenile corals at the study sites of Palk Bay.
S.No Genus V1 V2 M1 M2 P1 P2
1 Goniopora 1.5 0.0 0.0 0.0 0.0 2.4
2 Leptastrea 81.8 45.2 86.8 12.2 10.9 14.6
3 Porites 9.1 29.0 7.5 63.3 17.4 12.2
4 Favia 3.0 9.7 5.7 6.1 26.1 14.6
5 Favites 3.0 9.7 0.0 16.3 10.9 22.0
6 Cyphastrea 1.5 6.5 0.0 2.0 0.0 4.9
7 Goniastrea 0.0 0.0 0.0 0.0 32.6 4.9
8 Acropora 0.0 0.0 0.0 0.0 2.2 19.5
9 Galaxea 0.0 0.0 0.0 0.0 0.0 2.4
10 Hydnophora 0.0 0.0 0.0 0.0 0.0 2.4
0 1 2 3 4 5 6 7 8
V1 V2 M1 M2 P1 P2
Vedhalai Mandapam Pamban
Average Density m-2
29 | P a g e As per the results of Bray-Curtis cluster analysis under paired linkage, the study sites along the Palk Bay reef were grouped into 2 main clusters with 80%
similarity based on the taxonomic composition of juvenile corals (Fig 2.6). The study sites P1 and P2 were grouped together and the study sites V1, V2 and M2 were merged in one single group due to the similarity in the taxonomic composition of juvenile corals. The study site M3 differed from other study sites in the taxonomic composition of juvenile corals and form an individual cluster. SIMPER analysis showed that the taxonomic composition of the juvenile corals was highly dissimilar between Mandapam and Pamban with an average dissimilarity of 41.80%. Abundance of the juveniles of Goniastrea and Acropora sp had largely contributed to the observed differences in the taxonomic composition of the juveniles between the study sites in Pamban, Vedhalai and Mandapam (Table 3).
Fig 2.6. Bray-Curtis cluster analysis of the study sites at Palk Bay based on the taxonomic composition of the juvenile corals.
30 | P a g e Table 3- Results of SIMPER analysis and One-way ANOSIM (R value and Significance level) on the abundance (percent cover) of juvenile corals at the study sites of Palk Bay reef.
Vedhalai vs Mandapam
R value = -0.25; Level of Significance (%) = 100; Avg. dissimilarity= 21.70 Benthic component Average abundance Average
dissimilarity
%
contribution
Cum % Vedhalai Mandapam
Favites 1.54 1.01 6.01 27.70 27.70
Cyphastrea 1.35 0.60 4.82 22.21 49.91
Goniopora 0.55 0 3.20 14.77 64.68
Porites 2.03 2.24 3.20 14.77 79.44
Leptastrea 2.80 2.46 3.19 14.71 94.15
Vedhalai vs Pamban
R value = 1; Level of significance (%) = 10; Average dissimilarity- 36.10 Benthic component Average abundance Average
dissimilarity
%
contribution
Cum % Vedhalai Pamban
Goniastrea 0 2.09 9.09 25.17 25.17
Acropora 0 1.77 7.47 20.69 45.85
Cyphastrea 1.35 0.50 4.39 12.16 58.01
Leptastrea 2.80 1.79 4.37 12.11 70.12
Goniopora 0.55 0.86 2.88 7.99 78.11
Favia 1.54 1.94 1.97 5.47 83.57
Mandapam vs Pamban
R value = 0.917; Level of significance (%) = 10; Average dissimilarity- 41.80
Genus Average abundance Average
dissimilarity
%
contribution
Cum % Mandapam Pamban
Goniastrea 0 2.09 10.00 23.92 23.92
Acropora 0 1.77 8.19 19.59 43.51
Favites 1.01 1.91 5.24 12.53 56.04
Goniopora 0 0.86 3.86 9.24 65.28
Leptastrea 2.46 1.79 3.52 8.43 73.71
Cyphastrea 0.60 0.50 3.10 7.41 81.12
2.3.4. Size structure of juvenile corals
The overall distribution of juvenile corals of various size classes varied between the study sites. The percentage of juvenile corals of <1 mm and >3 mm size were high at the study sites of Vedhalai and Pamban respectively. Whereas, juvenile corals of size 1-3 mm was high in Mandapam. The percentage of juvenile corals of <1
31 | P a g e mm size varied between a minimum of 0 ± 13.8 at M1 to a maximum of 27.3 ± 13.5 at V1. Similarly, the juvenile corals of the size class 1-3 mm was high in M1 (67.9%
± 17.8) and low in P2 (32.1% ± 18). Juveniles corals of the size class 3-5 mm was high in P2 (51.8 ± 15.7) and low in V1 (19.7 ± 16.4) (Fig 2.7).
Fig 2.7. Average percentage composition of juvenile corals of different size classes at the study sites of Palk Bay.
2.3.5. Recruitment rate of corals
In total, 56 juvenile corals were recorded from the permanent quadrats deployed at all the study sites of Palk Bay during the study period. The rate of recruitment ranged between a minimum of 3 recruits 10 m-2 2 yrs-1 (M1) to a maximum of 12 recruits 10 m-2 2 yrs-1 (P2) across the study sites (Fig 2.8). The mean recruitment rate of the corals was high in Pamban (12 recruits 10 m-2 2yrs-1) followed by Mandapam (6 recruits 10 m-2 2yrs-1) and Vedhalai (5.5 recruits 10 m-2 2yrs-1).
Though the rate of recruitment showed variation, it does not differ significantly between the study sites (One-way ANOVA, F=1.4; Fcrit=2.24; p value = 0.2>0.05).
The size of the observed juveniles ranged between a minimum of 6 mm to a 0
20 40 60 80 100
V1 V2 M1 M2 P1 P2
Vedhalai Mandapam Pamban
Percentage
3-5 mm 1-3 mm 0-1 mm
32 | P a g e maximum of 10 mm in diameter. In-situ identification of the juveniles at species level was difficult due to their small size and poorly developed corallites.
Fig 2.8. Recruitment rate of corals in the natural substrate during the study period of two years (2013-14) at the study sites of Palk Bay reef. Error bars indicate standard error.
2.3.6. Survival and Mortality of juvenile corals
A maximum of 93.1% of the juvenile corals survived the sedimentation stress during NE monsoon period. In total, 41 of 600 tagged juveniles were dead post NE monsoon corresponding to a relative mortality percentage of 6.9%. Individual corallites of the dead juveniles were covered with sediment and sand particles (Fig 2.9). Mortality in response to sedimentation was high with Favia sp (9.7%) followed by Porites sp (8%) (Fig 2.10). An average of 94% juveniles in Vedhalai and 93%
juveniles each in Mandapam and Pamban survived the sedimentation stress during the NE monsoon. Though the survivability and mortality of the juvenile corals varied across the study sites along the Palk Bay reef, it did not show a statistically significant variation (One-way ANOVA, F=0.351; Fcrit= 2.57; p value 0.9>0.05). The survival
0 2 4 6 8 10 12 14 16
V1 V2 M1 M2 P1 P2
Vedhalai Mandapam Pamban
No of Recruits 10 m-2 2 yrs-1
